1. Field
The following description relates to an optical device, and more particularly, to an arrayed waveguide grating (AWG) device which is used as wavelength multiplexer/demultiplexer for optical signals in an optical communication system.
2. Description of Related Art
Arrayed waveguide grating (AWG) is a device used as wavelength multiplexer/demultiplexer for an optical signal in an optical communication system. AWG consists of a number of arrayed waveguides that are designed to increase in length from the shortest waveguide to the longest waveguide, so that for light traveling with a constant phase difference between the waveguides, constructive interference takes place on a particular output channel and destructive interference takes place on the other output channels, thereby resulting in the light being divided by wavelength.
If a phase of each of the arrayed waveguides has a different value from a designed phase, sufficient destructive interference may not be produced on the relevant channel, which leads to leakage of signal to other channels. Crosstalk due to the signal leakage is one of important factors that hamper the AWG performance.
A number of methods to improve the crosstalk performance have been suggested, for which one method increases process resolution, which takes a considerable amount of time and cost, while another method increases the width of arrayed waveguides or reduces an etching depth, but inevitably results in a higher-order mode when using a wide waveguide, whereby undesired peaks appear in a spectrum. Also, even when the etching depth is lowered, it is not easy to narrow the width of waveguides to the extent so that a single mode condition can be satisfied to achieve a desired performance. Generally, as a method for suppressing such higher-order modes, it has been known to insert a kind of mode filter that satisfies the single mode condition in the middle of the waveguide. Such a mode filter, however, uses a narrow waveguide and a taper, which may cause poor crosstalk performance and hence may be avoided to use. Also, in some cases, a layout in which the narrow waveguide is identically inserted all over the arrayed waveguide region may not be feasible.